Various research and development projects have actively been conducted with respect to exhaust gas post-treatment devices for vehicles equipped with diesel engines in order to meet the requirements of emission regulations such as EU6, EU6c, RDE and the like.
In particular, a selective catalytic reduction (SCR) catalyst is essentially required to respond to the RDE regulation. As a post-treatment device using such an SCR catalyst, a combination of a diesel oxidation catalyst (DOC) or a lean NOx trap (LNT), a diesel particulate filter (DPF), and the SCR catalyst has extensively been used.
The SCR catalyst (especially, Cu-SCR) may be converted into a sulfur oxide such as SO3 at a temperature of approximately 200-300° C. under 500° C., and the sulfur oxide may be adsorbed to the SCR device to result in a sulfur poisoning phenomenon. When a sulfur poisoning amount exceeds a predetermined level, the NOx purification performance of the catalyst may be degraded.
Meanwhile, when the temperature of the SCR catalyst is increased to 500° C. or higher, desulfation may naturally be performed. However, when a distance between SCR and DPF is increased according to vehicle specifications, the temperature of the SCR catalyst may not be sufficiently increased, and thus, the desulfation of SCR may not appropriately be performed. Therefore, the purification performance of the SCR catalyst may be degraded.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.